Measuring the carbon impact of healthcare interventions is essential if we're going to make the sector sustainable, however tracing all of the emmission from even a simple treatment can be tricky. Romi Haas, a research fellow at Monash Department of Clinical Epidemiology joins us to explain how it works, and how research could be more efficient. New U.S. guideline on breast cancer screening  have been extended to women in their 40s -  Katy Bell, from the University of Sydney, and Stacy Carter, from the University of Wollongong explain why the good intention of that change wont be mirrored in outcomes - and may even induce harm.   Reading list: Clinician and health service interventions to reduce the greenhouse gas emissions generated by healthcare: a systematic review  Breast cancer screening from age 40 in the US